What is a colonic polyp?

A polyp is a general name for a benign growth of the lining of any organ.

If the growth arises from the large bowel or colon, it is a colonic polyp.

Colonic polyps can be described and divided in various ways.

Number – single, two or multiple in the colon.

Size – diminutive (under 5mm) or large (under 2cm).

Site – exactly where in the colon they are, for example in the rectum only or throughout the bowel.

Shape – most polyps are on a stalk or pedunculated but others are flat called sessile.

Type – the most important division of colonic polyps is by cell type. This can most accurately be determined by examining the whole polyp or at least part of it under a microscope in the laboratory. This is called histological examination.

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Types of colonic polyp

Adenomatous polyps

The most important type of colonic polyp is the neo-plastic or adenomatous polyp.

Adenomatous polyps start as benign growths, but as they grow larger may become invasive and therefore can develop into cancerous polyps.

For this reason great efforts are made to detect such polyps, remove them for examination and therefore prevent cancerous change.

Most adenomatous polyps are pedunculated, which means they have a stalk that looks like a tree trunk.

Some polyps are flat or sessile with a velvety appearance spreading thinly over the bowel wall. Such polyps are often discovered to be villous adenomas.

In general the larger the polyp, the more likely there is to be malignant or cancerous change.

Hyperplastic polyps

Hyperplastic polyps are very common, but tend to be small. They are flat and shiny but are traditionally thought not to be neoplastic and do not develop into cancer.

If you have a hyperplastic polyp in your left colon that measures less than 1cm, you will not need to attend a follow-up appointment.

If you have a larger hyperplastic polyp or one in the right colon, this is a serrated polyp, you may require a colonoscopy to remove it and reduce the risk of cancer development.

Serrated polyps

These are polyps which have features that are present in hyperplastic polyps. But this type of polyp has malignant potential and it needs to be removed if discovered at colonoscopy.

They are typically found in the caecum and the ascending colon.

They are difficult to see and special careful inspection is required to identify them. Removal of such polyps is felt to be curative.

Careful examination of the polyp can distinguish this type of polyp from adenomatous polyps, but occasionally removal may be necessary to be certain.

Hamartomas

Hamartomatous polyps are composed of normal tissue but in an abnormal mixture. Hamartomas are like birth marks and tend to occur in children. They are therefore often called juvenile polyps.

A particular type of hamatomatous polyp is found in the Peutz-Jeghers syndrome often associated with abnormal freckling of the lips.

Peutz-Jeghers polyps can present with small bowel obstruction and produce abdominal pain. They may become malignant and any polyps discovered to be under 1cm should be removed.

Peutz-Jeghers polyps occur through out the gastrointestinal tract, not just the colon and they do carry a definite cancer risk.

Patients with Peutz-Jeghers syndrome require a regular surveillance endoscopy, colonoscopy and wireless capsule endoscopy and if treatment is required, this often takes place in a specialist gastroenterological centre.

What causes polyps?

Colonic polyps are caused by alterations in the genes that code for important proteins in the cell. The more gene mutations a cell acquires the more likely it is to become cancerous.

However, the cells in sporadic colon cancers require a number of gene mutations before a cell becomes an adenoma and further gene mutations in these adenoma cells can result in the progression to cancer.

It is clear that the older you get the more likely you are to have colonic polyps (eg 30 per cent of people over 60 years old will have an colonic adenoma).

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Environmental factors in Western civilisation, particularly a diet high in red meat, fat and low in fibre, has been suggested as important factors in developing colonic polyps.

A few rare patients have a genetic or inherited tendencies to develop colonic polyps, often at a young age.

The most important of these disease is familial adenomatous polyposis (FAP), when hundreds of colonic polyps occur by the age of 20 years. This requires an operation to remove the colon, called a colectomy, which nearly always takes place before 30 years of age.

Why are colonic polyps important?

It is believed that over a long time period, probably three years or more, some adenomatous polyps may grow and start to invade the bowel wall and become colonic cancer.

For this reason it is important to identify and remove these polyps to prevent colon cancer developing.

Colonic polyps may produce symptoms without becoming cancer (eg rectal bleeding or change in bowel habit). At this stage they may be removed at colonoscopy.

What symptoms do polyps cause?

Most colonic polyps cause no symptoms.

The larger the polyp and the nearer the anus or end of the bowel the more likely the patient will notice symptoms. By far the most frequent is rectal bleeding or iron deficiency anaemia.

Some large flat villous polyps especially in the rectum can cause diarrhoea. Only rarely do colonic polyps cause pain.

Unfortunately this means significant polyps can still be present, especially on the right side of the colon away from the anus, without any symptoms.

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Identifying these polyps is important but they can only be detected by testing for occult (or concealed) bleeding or by colonoscopy that is telescopic examination of the whole large bowel starting at the rectum.

How is the diagnosis made?

Some patients may have symptoms due to polyps leading to investigation of the colon. Others may have polyps found while undergoing colon tests for unrelated symptoms.

Increasingly, colonic polyps are being identified by surveillance programmes, which attempts to detect polyps early before any symptoms.

Currently, the entire UK population aged between 60 to 74 are entered into the bowel cancer screening programme by providing a stool sample which is tested for the presence of blood (called faecal occult blood test (FOBT).

A positive test results in the patient being offered a colonoscopy. Up to 50 per cent of patients testing FOB positive will have an adenoma and 10 per cent will have a colon cancer.

In addition, the UK government is starting to roll out the 'Bowel Scope' programme.

This invites all people aged 55years of age to undergo a flexible sigmoidoscopy. Any individual with an advanced adenoma (defined as a polyp under 1cm, with high grade dysplasia or with villous histology) are offered a colonoscopy.

This government sponsored NHS scheme attempts to find polyps or even colon cancer early before symptoms by testing the faeces or motions for occult blood loss.

How is the diagnosis made?

Colonic polyps are most often seen directly during colonoscopy or flexible sigmoidoscopy.

Sampling (biopsy) or total removal of the polyp is then possible to determine the polyp type.

Polyps may be detected by barium enema, a type of X-ray of the bowel, or CT colonography. These techniques do not allow determination of cell type or for the polyp to be removed.

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What is the treatment?

Polypectomy

Most polyps can be removed during colonoscopy whilst the patient is sedated. This is done by passing a wire snare down the colonoscopy, looping and tightening the snare around the stalk of the polyp then passing an electric current through the wire.

This coagulates the blood vessels and then cuts through the stalk. The polyp is then usually sent to the pathology laboratory for microscopic examination.

Flat, sessile or villous polyps can be removed by a newer technique called endoscopic mucosal resection (EMR).

With this technique the flat polyp is lifted off the colonic wall by injection beneath of a special solution. This produces a temporary artificial cushion to enable safe use an electrical snaring, reducing the risk of perforation. The injected solution is quickly reabsorbed.

Polypectomy is painless because the colonic nerves are only sensitive to stretching.

Polypectomy is safe but carries a risk of perforation (going through the bowel wall) in about one case in 300.

Bleeding occurs in 1 per cent of cases after polypectomy. Bleeding usually stops by itself by can require blood transfusion and further treatment.

Clearly the larger the polyp the greater the risk.

Surgery

Occasionally a polyp is too large to be removed endoscopically without an unacceptably high risk of bleeding or perforation.

Removal by surgery that opens up the abdomen can be the safest option to ensure complete removal and cure.

Large rectal polyps can sometimes be removed through the anus under general anaesthetic without the need to cut open the abdomen.

What follow up is needed after polypectomy?

People with adenomatous polyps are likely to grow further polyps. Follow-up however is determined by a number of factors: the size, type and number of polyps; whether poylpectomy has been complete; the general health and age of the patient and of course, the patient's individual wishes.

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Routinely repeat colonoscopy will be around three years after the colon has been cleared of significant polyps but may be between one and five years dependent on the factors above.

Can colonic polyps be prevented?

There is at present no conclusive evidence that dietary changes or supplements that will prevent colonic polyps from being formed.

Drug treatments are not proven to be of benefit and are not routinely advised.

What is the prognosis (outlook)?

Patients with polyps that can be safely identified and removed entirely can be reassured they have an excellent outlook.

Occasionally polyps cannot be removed endoscopically and require surgery. If surgery is successful and there is no malignant change the outlook is also excellent.

The most important aspect of prognosis is continued vigilance and surveillance with colonoscopy to detect any new colonic polyp formation during an entire patient's lifetime.

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